Short-term in situ immobilization of Cd and Ni by beringite and steel shots application to long-term sludged plots

Beringite and steel shots were mixed with the upper 20 cm of the soil. One year after addition, the extractability in calcium nitrate (0.1 M) and the plant availability of soil-Cd and Ni were investigated. The addition of beringite (5 % w/w) and steel shots (1 % w/w) led to a lower extractability of Cd and Ni. In the most contaminated plots, the extractability of Cd and Ni after 1 year had decreased, respectively, 54 % and 53 % for beringite and 41 % and 40 % for steel shots. The metal content in different organs of maize plants (shoots, sixth leaf, ear leaf and grains), grown on the field trial, was determined. The Cd transfer from soil to plant decreased following the addition of beringite, except in the most contaminated plots. No decreased soil-plant transfer of Cd was observed after the addition of steel shots. Both the addition of beringite and steel shots led to a lower Ni transfer to the maize aerial organs and grains. No phytotoxicity or deficiency symptoms due to the additives were observed on the plants. The addition of beringite and steel shots seems promising to lower the soil-plant transfer of Ni at such metal contaminated soils. The depth of mixing and the method of application of the soil additives in the field appear to be very significant variables; additional comparative tests are needed, however. ((C) Inra/Elsevier, Paris.).